1. Field of the Invention
The present invention relates to an acceleration estimation device that estimates vehicle acceleration, and a vehicle including the same.
2. Description of the Background Art
The traveling speed of a vehicle can be calculated on the basis of the rotational speeds of its wheels. When the vehicle is rapidly accelerated, however, the wheels may be rotated while slipping on a road surface. When the vehicle is rapidly decelerated (braked), the wheels may be caused to slide on the road surface. In such a case, the speed of the vehicle that can be calculated from the rotational speed of the wheels does not coincide with the actual traveling speed of the vehicle.
Therefore, the acceleration of the vehicle is detected using an acceleration sensor, and the detected acceleration is integrated to calculate the speed of the vehicle.
When the vehicle is rapidly accelerated or decelerated, however, the vehicle body is inclined up and down in a traveling direction by pitching of the vehicle body. That is, the front of the vehicle body rises at the time of the rapid acceleration, and lowers at the time of the rapid deceleration. Thus, the forward-and-backward acceleration of the vehicle that is detected by the acceleration sensor does not accurately coincide with an acceleration in a traveling direction of the vehicle.
JP 10-104259 A discloses a vehicle longitudinal acceleration estimating device that removes an unnecessary component of an acceleration sensor for detecting a longitudinal acceleration to calculate an estimated value of the longitudinal acceleration.
In the longitudinal acceleration estimating device disclosed in JP 10-104259 A, the change in an output voltage of the acceleration sensor is frequency-analyzed and is classified into changes due to DC offset, changes due to temperature drift, changes due to road conditions, changes due to acceleration/deceleration of the vehicle, and changes due to pitching of the vehicle body. A Karman filter is used to extract only a variable component having a higher frequency than a particular frequency from a detected value of the longitudinal acceleration by the acceleration sensor.
This causes a variable component due to DC offset and a variable component due to temperature drift respectively having low frequencies to be removed from the detected value of the longitudinal acceleration. As a result, the estimated value of the longitudinal acceleration is not affected by changes with time and changes in temperature.
In the longitudinal acceleration estimating device disclosed in JP 10-104259A, an unnecessary component in a particular frequency band can be removed from the detected value in the acceleration sensor. Consequently, it is considered that only a variation component in the particular frequency band is removed from the detected value in the acceleration sensor to remove the variation component due to pitching of the vehicle body.
However, a variation component due to pitching in a frequency band other than the particular frequency band cannot be removed. Therefore, the longitudinal acceleration of the vehicle cannot be accurately estimated when the vehicle is accelerated and decelerated.
On the other hand, JP 8-268257A discloses an actual speed estimator that estimates an actual vehicle speed of a vehicle. In the actual speed estimator, a coefficient of rolling rigidity and a coefficient of pitching rigidity are defined to correct an output of a crosswise acceleration sensor and an output of a lengthwise acceleration sensor using the coefficient of rolling rigidity and the coefficient of pitching rigidity.
However, the variation in a pitch angle at the time of the acceleration and deceleration of the vehicle is not constant. In the actual speed estimator disclosed in JP 8-268257 A, the relationship between the output of the lengthwise acceleration sensor and the pitch angle is determined by the coefficient of pitching rigidity. Therefore, the acceleration in a traveling direction of the vehicle cannot be accurately estimated in correspondence with arbitrary pitching of the vehicle.